Most people are only familiar with the lunar dynasty king Yayati, who was cursed with old age by Sukracharya (guru of the Asuras) and regained his youth by giving his old age to his youngest son Puru. Puru, along with Yayati's eldest son Yadu, started two of the most famous royal families, the Pauravas and the Yadavas. Less famous, however, is Yayati's father Nahusha. Nahusha was such a good king on Earth that when Indra temporarily abandoned his post, the gods chose Nahusha to serve as the new king of the three worlds. But Nahusha was soon corrupted by his power, so the sage Agastya cursed him to become a large snake. Nahusha was only freed from the curse when he had a conversation with the Pandava Yudishthira about the proper way he should have lived his life, as described in the Vana Parva of the Mahabharata.
But my question is about Nahusha's wife. I gather from several sources that his wife was Viraja, a mind-born daughter of the Pitris, or ghosts of departed ancestors.
Here is what the Harivamsa says, for instance:
the ancestors of Kardama Prajapati are the descendants of Pulaha Prajapati, and these are the fatherly gods collectively termed as Susvadhas ... [T]he brainchild of this group of manes is lady Viraja who is the mother of king Yayati and the wife of King Nahusha.
A later chapter of the Harivamsa says the same thing:
King Nahusha begot six sons through a damsel of fatherly gods, known as lady Viraja, or lady Suswadha, to wit, these six Indra-like sons are: Yati, Yayati, Samyati, Ayati, Bhava, and Suyati
And it's also mentioned in this excerpt from the Anushanga Pada of the Vayu Purana:
Ayjapas were the Pitris of Kardama, the Prajapati, who was born of Pulaha. They were born of him again.... Groups of Vaishyas who are desirous of benefit, revere these in Shraddha. Their mental daughter is famous by the name of Viraja. The chaste lady was the wife of Nahusha and the mother of Yayati.
So my question is, what is the story of how a human king Nahusha married a daughter of the Pitris? The group of Pitris that Viraja was born from is apparently only worshipped by Vaishyas, not Kshatriyas, so I don't know how Nahusha would have encountered these Pitris or their daughter. Are there any scriptures that discuss this.
By the way, as I discuss in this answer, there is a story in the Padma Purana where instead of Viraja, Nahusha's wife is said to be Shiva and Parvati's daughter Ashokasundari. But given all the scriptural evidence I've given above, that story might be an interpolation.
